US10337955B2ActiveUtilityA1
Method for characterizing mode group properties of multimodal light traveling through optical components
Est. expiryJun 17, 2034(~7.9 yrs left)· nominal 20-yr term from priority
G01J 9/00G01J 2009/004G01M 11/338G02B 6/0365G02B 6/0288G02B 6/14G01J 2009/006
72
PatentIndex Score
1
Cited by
20
References
12
Claims
Abstract
The invention concerns a method for characterizing mode group properties of multimodal light traveling through an optical component, comprising: providing a Mode Group Separating optical fiber in an optical path between a light source and said optical component; launching reference pulses of light with a wavelength λt from said light source through said Mode Group Separating optical fiber into said optical component at discrete intervals between a core center and a core radius of said fiber. The Mode Group Separating optical fiber is a multimode fiber with an α-profile graded index core with an α-value chosen such that said fiber satisfies the following criterion at the wavelength λt: Δτ · L Δ T REF > 4 where: Δτ is a time delay difference between consecutive mode groups; L is a length of said fiber; ΔT REF is a Full Width at Quarter Maximum of said reference pulses.
Claims
exact text as granted — not AI-modifiedThe invention claimed is:
1. A method for characterizing mode group properties of multimodal light traveling through an optical component, wherein said method comprises the steps of:
providing a Mode Group Separating optical fiber ( 5 ) in an optical path between a light source ( 1 ) and said optical component ( 8 );
launching reference pulses of light with a wavelength λ t from said light source ( 1 ) through said Mode Group Separating optical fiber ( 5 ) into said optical component ( 8 ) at radial offsets between a core center and a core radius of said Mode Group Separating optical fiber;
detecting a light signal output by said optical component ( 8 );
wherein said Mode Group Separating optical fiber is a multimode fiber with an α-profile graded index core with an α-value chosen such that said Mode Group Separating optical fiber satisfies the following criterion at the wavelength λ t :
Δτ
·
L
Δ
T
REF
>
4
where:
Δτ is a time delay difference between consecutive mode groups expressed in ps/m;
L is a length of said Mode Group Separating optical fiber expressed in m;
ΔT REF is a Full Width at Quarter Maximum of said reference pulses expressed in ps, where the Full Width at Quarter Maximum of a reference pulse is the difference between the two time values at which the power of the reference pulse is equal to quarter of its maximum value.
2. The method according to claim 1 , comprising:
measuring a Dispersion Modal delay profile for said Mode Group Separating optical fiber, called a reference DMD profile;
measuring a Dispersion Modal delay profile at the output of said optical component, called a resulting DMD profile;
comparing said reference DMD profile and said resulting DMD profile in order to characterize the mode group properties of multimodal light traveling through said optical component.
3. The method according to claim 1 , wherein said Mode Group Separating optical fiber satisfies the following criterion at the wavelength λ t :
Δτ
·
L
Δ
T
REF
>
5.
4. The method according to claim 1 , wherein said wavelength λ t is between 800 nm and 1500 nm.
5. The method according to claim 1 , wherein said Mode Group Separating optical fiber has a core diameter of 50 μm ±2.5 μm and a numerical aperture NA=0.2 ±0.015, and wherein:
Δτ(λ,α)= p 00 +p 10 *λ+p 01 * α+p 11 *λ*α+p 02* α 2
with:
p00 between −1.461 and −1.116
p10 between −0.001516 and −0.00128
p01 between 1.061 and 1.317
p11 between 0.0006583 and 0.0007706, and
p02 between −0.3125 and −0.2581.
6. The method according to claim 5 , wherein:
p00 =−1.288
p10 =−0.001398
p01 =1.189
p11 =0.0007145
p02 =−0.2853.
7. The method according to claim 1 , wherein said Mode Group Separating optical fiber is a Few Mode optical fiber comprising an optical core having a radius R 1 and a maximal refractive index n 0 and an optical cladding surrounding the optical core,
said optical cladding having at its outer edge a refractive index n Cl ,
wherein said optical cladding comprises an inner cladding layer directly surrounding said optical core, with an inner radius R 1 and an outer radius R 2 ≥R 1 , said inner cladding layer having a constant refractive index n 2 =n Cl , and a region of depressed refractive index n trench ,called a trench, surrounding said inner cladding layer, said trench having an inner radius R 2 , with R 2 ≥R 1 , and an outer radius R 3 , with R 3 >R 2 .
8. The method according to claim 7 , wherein:
R
1
=
14
µm
±
0.5
µm
Δ
1
=
(
n
0
2
-
n
Cl
2
)
2
n
0
2
=
0.705
%
±
0.04
%
R
2
=
15.3
µm
±
0.5
µm
R
3
=
21.4
µm
±
0.5
µm
Δ
n
3
=
n
trench
-
n
Cl
=
-
5
⨯
10
-
3
±
0.5
⨯
10
-
3
and wherein :
Δτ(λ,α) = p 00 + p 10*λ +p 01 *α+p 11 *λ*α+p 02*α 2
with :
p00 between −1.947 and −1.604
p10 between −0.001977 and −0.001743
p01 between 1.389 and 1.644
p11 between 0.0009262 and 0.001038, and
p02 between −0.3776 and −0.3235.
9. The method according to claim 8 , wherein:
p00=−1.776
p10=−0.00186
p01=1.517
p11=0.000982
p02=−0.3505.
10. The method according to claim 1 , wherein L=550 m and ΔT REF =40 ps.
11. The method according to claim 1 , wherein said optical component comprises:
a Variable Optical Attenuator (VOA);
an optical fiber;
a coupler; or
a detector.
12. The method according to claim 1 , comprising:
collecting light output by said optical component into a second Mode Group Separating optical fiber;
and wherein said second Mode Group Separating optical fiber is a multimode fiber with an α-profile graded index core with an α-value chosen such that said Mode Group Separating optical fiber satisfies the following criterion at the wavelength λ t :
Δτ
·
L
Δ
T
REF
>
4
where:
Δτ is a time delay difference between consecutive mode groups expressed in ps/m;
L is a length of said Mode Group Separating optical fiber expressed in m;
ΔT REF is a Full Width Quarter Maximum of said reference pulses expressed in ps.Cited by (0)
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